Robot-aided grinding apparatus
Described is an apparatus for robot-aided grinding, comprising the following: a manipulator, a linear actuator, and a grinding machine which includes a rotating grinding tool and is connected to the manipulator via the linear actuator. The apparatus further comprises a protective cover that partially surrounds the rotating grinding tool, the rotating grinding tool protruding from the protective cover at least on a first side. An adjusting mechanism is provided which connects the protective cover to the grinding machine and is designed to adjust the position of the protective cover in relation to the grinding machine.
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This disclosure relates to aspects of a robot-supported grinding apparatus in which a grinding machine with a rotating grinding tool is guided by a manipulator (e.g. an industrial robot).
BACKGROUNDGrinding and polishing processes are playing an increasingly important part in the surface finishing of workpieces. In automated, robot-supported manufacturing, industrial robots are being employed, with the aid of which, e.g. grinding processes can be automated.
In robot-supported grinding apparatuses, a grinding machine with a rotating grinding tool (e.g. grinding disc) is guided by a manipulator, for example, an industrial robot. During the grinding process, the so-called TCP (Tool Center Point) moves along an (in advance programmable, e.g. by means of Teach-In) path (trajectory). The specified path of the TCP determines, for every point in time, the position and orientation of the TCP, and thus of the grinding machine, as well. The robot control that controls the movement of the manipulator therefore generally includes a position control.
For surface finishing processes such as grinding, polishing, etc. it is usually not sufficient to only control the position of the tool, as the processing force (the force between the tool and the workpiece) also plays an important role in the finishing results. For this reason, the tool is generally not rigidly connected to the TCP of the manipulator, but rather via an elastic element which, in the simplest case, may be a spring. In order to adjust the processing force, in many cases a regulation (closed loop control) of the processing force is needed. For the purpose of implementing a force control, the elastic element can be a separate linear actuator that is mechanically coupled between the TCP of the manipulator and the tool (e.g. between TCP and a grinding machine on which a grinding disc is mounted). The linear actuator can be relatively small in comparison to the manipulator and is used, for the most part, to control the processing force while the manipulator moves the tool (together with the linear actuator) along the previously programmed trajectory in a position-controlled manner.
In practice, the wear of the tool may cause problems, e.g. during grinding. A grinding disc becomes worn in the course of the grinding process, as a result of which the diameter of the grinding disc is reduced. As a consequence of this, not only is the circumferential speed (which may also be a relevant processing parameter) reduced, but the position of the grinding machine (in particular that of the axis of rotation of the grinding tool) relative to the surface of the workpiece is also changed. The more the grinding disc is worn down, the closer the grinding machine must be brought to the surface of the workpiece.
The aforementioned wear-related reduction of the size of the grinding tool (grinding disc) has, among others, two consequences. In certain situations, when the trajectory of the TCP has been previously specified, the grinding tool may contact the workpiece surface late (and consequently at the wrong point). Furthermore, the size of the gap between the workpiece surface and any possibly existing protective cover that is mounted on the grinding machine and partially surrounds the grinding disc also changes. The size of this gap influences the effectiveness of a possibly existing suction system (for the removal of grinding dust).
Various embodiments described herein are directed to a robot-supported grinding apparatus that at least partially compensates for the negative or undesired influences resulting from the wear of the grinding tool as well as to related methods.
SUMMARYAn apparatus for robot-supported grinding is described. In accordance with one embodiment, the apparatus comprises the following: a manipulator, a linear actuator and a grinding machine with a rotating grinding tool. The grinding machine is coupled with the manipulator via the linear actuator. Further, the apparatus comprises an end stop that defines the maximum deflection of the linear actuator, wherein the position of the end stop is adjustable.
In accordance with a further embodiment the apparatus for robot-supported grinding comprises the following: a manipulator, a linear actuator and a grinding machine with a rotating grinding tool, wherein the grinding machine is coupled with the manipulator via the linear actuator. The apparatus further comprises a protective cover that partially surrounds the rotating grinding tool, wherein the rotating grinding tool protrudes from the protective cover on at least one side. A positioning device is provided that connects the protective cover to the grinding machine and that is designed to adjust the position of the protective cover relative to the grinding machine.
In accordance with another embodiment, the apparatus for robot-supported grinding comprises the following: a manipulator, a linear actuator and a grinding machine with a rotating grinding tool, wherein the grinding machine is coupled with a TCP of the manipulator via the linear actuator. The apparatus further comprises a protective cover that partially surrounds the grinding tool. The protective cover is rigidly connected to the TCP of the manipulator such that the rotating grinding tool protrudes from the protective cover on at least one first side.
Further, a method for operating a robot-supported grinding device comprising a manipulator, a linear actuator with an adjustable end stop and a grinding machine with a rotating grinding tool is described. Here the grinding machine is coupled with the manipulator via the linear actuator. In accordance with one embodiment, the method comprises adjusting a position of the end stop that defines the maximum deflection of the linear actuator.
In accordance with a further embodiment, the method comprises pressing the grinding tool against a reference surface with the aid of the manipulator, wherein at the same time a first side of a protective cover rests against a stop (41). The protective cover surrounds the grinding tool at least partially and the rotating grinding tool protrudes from the protective cover on at least one side.
Various embodiments are described in greater detail in the following using the examples shown in the figures. The figures are not necessarily true to scale and the invention is not limited to the illustrated aspects. Instead, emphasis is given to illustrating the underlying principles of the embodiments described herein. With regard to the figures:
Before describing the various embodiments in detail, a general example of a robot-supported grinding apparatus will be described. This comprises a manipulator 1 (for example, an industrial robot) and a grinding machine 10 with rotating grinding tool (grinding disc), wherein the grinding machine 10 is coupled with the tool center point (TCP) of the manipulator 1 via a linear actuator 20. In the case of an industrial robot having six degrees of freedom, the manipulator may consist of four segments 2a, 2b, 2c and 2d, each of which is connected via joints 3a, 3b and 3c. The first segment is usually rigidly connected to the base B (which, however, need not necessarily be the case). The joint 3c connects the segments 2c and 2d. The joint 3c may be biaxial and allow for rotation of the segment 2c around a horizontal axis of rotation (elevation angle) and around a vertical axis of rotation (azimuth angle). The joint 3b connects the segments 2b and 2c and allows for a swivel movement of the segment 2b relative to the position of the segment 2c. The joint 3a connects the segments 2a and 2b. The joint 3a can be biaxial, thus (similar to the joint 3c) allowing for a swivel movement in two directions. The TCP has a permanent position relative to the segment 2a, wherein this usually includes a rotational joint (not shown) that allows for a rotational movement around a longitudinal axis A (designated in
The manipulator 1 is usually position-controlled, i.e. the robot control can determine the pose (position and orientation) of the TCP and can move the latter along a previously defined trajectory. When the actuator 20 rests against an end stop, the pose of the TCP also defines the pose of the grinding tool. As mentioned early on, the actuator 20 serves to adjust the contact force (processing force) between the tool (grinding disc 11) and the workpiece W to a desired value during the grinding process. Controlling the processing force directly via the manipulator 1 is generally too imprecise for grinding applications because, due to the high inertia of the segments 2a-2c of the manipulator 1, quickly compensating force peaks (e.g. when the grinding tool contacts the workpiece 40) using common manipulators is virtually impossible. For this reason, the robot control is configured to control the pose (position and orientation) of the TCP, whereas controlling the contact force (see also
As already mentioned, the contact force FK between the tool (grinding disc 11) and the workpiece W can be adjusted during the grinding process with the aid of the (linear) actuator 20 and a force control unit (which, for example, may be implemented in the control 4) so that the contact force FK between grinding tool and workpiece W corresponds to a specifiable desired value. Thereby the contact force is a reaction to the actuator force FA with which the linear actuator 20 presses against the workpiece surface S (see also
The actuator may be a pneumatic actuator, e.g. a double-acting pneumatic cylinder. Other pneumatic actuators, however, are also applicable such as, e.g. bellows cylinders and air muscles. As an alternative, direct electric drives (gearless) may also be considered. In the case of a pneumatic actuator, the force control itself can be realized using a control valve, a regulator (implemented in the control 4) and a compressed air reservoir. The specific implementation, however, is of no importance for the further description and will therefore not be discussed in detail.
In the case depicted in
The embodiment shown in
In contrast to what was described above with regard to
Instead of a snap-in locking device, any other positioning device by means of which the protective cover 12 can be fixated at various positions (relative to the grinding machine 10) can also be used. One possible alternative would be, e.g. a self-retaining positioning device with which the distance b (see
Since the grinding disc becomes smaller during normal operation, it is enough for the positioning device (e.g. the snap-in locking device 13) to only allow for an adaptation of the position of the protective cover 12 (i.e. the distance b) in one direction—towards smaller distances b—wherein, when the grinding disc 11 is replaced, the positioning device is reset at its maximum distance (bMAX). The snap-in locking device may therefore also include at least one locking latch that allows the position to be linearly adjusted in one direction (towards smaller distances b) while adjustment of the position in the other direction (towards greater distances b) is blocked by the locking latch (similar to a ratchet, see also
A situation is now assumed in which the protective cover 12 is, at the beginning, so adjusted that the gap size c with a new, unworn grinding disc 11 having a diameter d0 (e.g. d0=150 mm) corresponds exactly to the desired value cREF (c=cREF). After a few rounds of grinding, the grinding disc is partially worn and the diameter of the grinding disc 11 has been reduced to a value of d1 (e.g. d1=140 mm), as a result of which the size of the gap c has also been reduced (e.g. by 10 mm, c<cREF). In order to enlarge the gap size c back to its original value, the distance b must be adapted (in the present example, b would have to be reduced by 10 mm). In order to be able to automatedly adjust the snap-in locking device 13, which does not require its own drive, when the grinding disc becomes partially worn, a support plane 40 (e.g. a plane reference surface) is located near the manipulator (e.g. next to the workpiece W in the robot cell) on which at least one stop 41 is arranged. The stop 41 defines a plane that lies parallel to the support plane 40 and that is at a distance to the latter that corresponds to the desired value cREF. The manipulator 1 is programmed to periodically (e.g. after every or every second grinding operation) move the grinding machine 10 towards the support plane 40 and into a reference position, pressing the grinding disc 11 against the support plane 40—similarly to being pressed against a workpiece but while the grinding disc is not rotating. The at least one stop 41 is arranged such that when the grinding machine is in the reference position—the bottom side of the protective cover 12 rests against the at least one stop 41. By pressing the grinding disc 11 against the support plane 40 (reference surface), the protective cover 12 is pushed upwards until the gap size c once again (approximately) corresponds to the desired value cREF.
The adjustment procedure for the gap size cREF is illustrated in
In
In the example shown in
As, in the present embodiment, the protective cover 12 is rigidly connected to the TCP of the manipulator 1 (i.e. not via the actuator 20), the gap size c does not depend on the diameter of the grinding disc 11, but instead depends only on the pose of the TCP relative to the surface S of the workpiece (see
In
In
A different approach is depicted in
With the embodiments illustrated
The examples in
The positioning element for adjusting the end stop EA can also be formed by the actuator 20 and a completely passive element (such as, e.g. a brake or blocking element). The example shown in
In order to adjust the position of the end stop EA, the manipulator can move the TCP to a given reference position (distance) relative to a reference surface S (as, e.g. in
Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.
Claims
1. An apparatus for robot-supported grinding, the apparatus comprising:
- a manipulator;
- a linear actuator;
- a grinding machine with a rotating grinding tool, the grinding machine being coupled with the manipulator via the linear actuator;
- an end stop that defines a maximum deflection of the linear actuator, wherein a position of the end stop is adjustable; and
- a control configured to adjust the end stop based on a size of the rotating grinding tool.
2. The apparatus of claim 1, wherein the control is configured to adjust the end stop using a positioning element.
3. The apparatus of claim 2, wherein the positioning element comprises a rod blocking device.
4. The apparatus of claim 3, wherein the control is configured to disengage the rod blocking device, move a tool center point of the manipulator into a reference position in which the rotating grinding tool contacts a surface, and activate the rod blocking device in order to fixate the position of the end stop.
5. The apparatus of claim 2, wherein the positioning element includes a linear electric drive.
6. The apparatus of claim 1, wherein the control is configured to adjust the position of the end stop based on a diameter of the rotating grinding tool.
7. The apparatus of claim 1, wherein the control is configured to move a tool center point of the manipulator into a reference position in which the rotating grinding tool contacts a surface, and to adjust the position of the end stop such that a current deflection of the linear actuator equals the maximum deflection defined by the position of the end stop.
8. The apparatus of claim 1, wherein the control is configured to move a tool center point of the manipulator into a reference position in which the rotating grinding tool contacts a surface, and to adjust the position of the end stop in dependency on a current deflection of the linear actuator.
9. A method for operating a robot-supported grinding apparatus that comprises a manipulator, a linear actuator with an adjustable end stop and a grinding machine with a rotating grinding tool, the grinding machine being coupled with the manipulator via the linear actuator, the method comprising:
- defining a maximum deflection of the linear actuator by the end stop of the linear actuator; and
- adjusting a position of the end stop of the linear actuator based on a size of the rotating grinding tool.
10. The method of claim 9, wherein the rotating grinding tool is a grinding disc and the position of the end stop is adjusted based on a diameter of the grinding disc.
11. The method of claim 9, wherein adjusting the position of the end stop comprises:
- moving a tool center point of the manipulator into a reference position in which the rotating grinding tool contacts a surface; and
- adjusting the position of the end stop such that a current deflection of the linear actuator equals the maximum deflection defined by the position of the end stop.
12. The method of claim 9, wherein adjusting the position of the end stop comprises:
- moving a tool center point of the manipulator into a reference position in which the rotating grinding tool contacts a surface; and
- adjust the position of the end stop in dependency on a current deflection of the linear actuator.
13. The method of claim 9, wherein adjusting the position of the end stop comprises:
- disengaging a rod blocking device to enable shifting the position of the end stop;
- moving a tool center point of the manipulator into a reference position in which the rotating grinding tool contacts a surface; and
- activating the rod blocking device to fixate the position of the end stop.
14. An apparatus for robot-supported grinding, the apparatus comprising:
- a manipulator;
- a linear actuator;
- a grinding machine with a rotating grinding tool, the grinding machine being coupled with the manipulator via the linear actuator;
- an end stop that defines a maximum deflection of the linear actuator, wherein a position of the end stop is adjustable;
- a rod blocking device coupled to the end stop; and
- a control configured to disengage the rod blocking device, move a tool center point of the manipulator into a reference position in which the rotating grinding tool contacts a surface, and activate the rod blocking device in order to fixate the position of the end stop.
15. A method for operating a robot-supported grinding apparatus that comprises a manipulator, a linear actuator with an adjustable end stop and a grinding machine with a rotating grinding tool, the grinding machine being coupled with the manipulator via the linear actuator, the method comprising:
- defining a maximum deflection of the linear actuator by the end stop of the linear actuator; and
- adjusting a position of the end stop of the linear actuator by: disengaging a rod blocking device to enable shifting the position of the end stop; moving a tool center point of the manipulator into a reference position in which the rotating grinding tool contacts a surface; and activating the rod blocking device to fixate the position of the end stop.
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Type: Grant
Filed: Apr 4, 2017
Date of Patent: Oct 10, 2023
Patent Publication Number: 20190111570
Assignee: FerRobotics Compliant Robot Technology GmbH (Linz)
Inventor: Ronald Naderer (Oberneukirchen)
Primary Examiner: Joel D Crandall
Assistant Examiner: Michael A Gump
Application Number: 16/090,534
International Classification: B25J 11/00 (20060101); B24B 27/00 (20060101); B25J 9/10 (20060101); B25J 9/12 (20060101);